This application claims the priority of Korean Patent Application No. 2003-23066, filed on Apr. 11, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fuel amount control system for a fuel cell, which includes a sensor, and more particularly, to a fuel amount control system suitable for a smaller fuel cell, which includes a small sensor to measure the concentration of fuel supplied to the fuel cell to maintain a constant fuel concentration.
2. Description of the Related Art
Fuel cells are electrochemical systems in which a free energy change resulting from fuel oxidation and reduction is converted into electrical energy. A fuel cell consists of three elements, i.e., an anode where an oxidation reaction takes place, a cathode where a reduction reaction takes place, and an electrolyte disposed between the anode and the cathode to carry ions. In the anode, a fuel, such as hydrogen or methanol, loses electrons and is transformed into cations. In the cathode, oxygen ions in air accept the electrons supplied from the anode and produce water.
Fuel cells that directly utilize liquid methanol as a fuel source are called direct methanol fuel cells (DMFCs). In DMFCs, a mixture of methanol and water in a predetermined ratio is directly supplied to an anode of a fuel cell stack, so that a separate fuel modifier is not required and the fuel cell system has a smaller size. However, when a concentration of a methanol solution supplied to the stack is beyond an appropriate range, the overall energy generation efficiency of the fuel cell decreases. Conventionally, using various kinds of sensors capable of detecting the concentration of the methanol solution supplied to the anode have been suggested to improve the performance of DMFCs.
U.S. Pat. No. 6,303,244 discloses a methanol sensor attached to a fuel tank but does not disclose a detailed method of detecting the concentration of methanol. U.S. Pat. No. 6,488,837 discloses a method of measuring methanol concentration by using a current sensor that outputs an electrical signal depending on methanol concentration and is connected to a small circuit that traverses a cathode and an anode. International Patent No. 0123,874 discloses a method of measuring methanol concentration, in which a portion of a methanol solution is extracted from a fuel cell and heated to the boiling point prior to measurement. Korean Patent Publication No. 2002-0056136 discloses a sensor that detects methanol concentration based on variations in the absorbance of a methanol solution.
In the above patents, a separate methanol sensor increases the size of the fuel cell system. In addition, there is no prominent improvement in energy efficiency.